Models nitrogenase

Palmer, J.G., Doemeny, P. A., and Schrauzer, G. N. (2001), The chemical evolution of a nitrogenase model, XXIII. The nature of the active site and the role ofhomocitric acid in MoFe-nitrogenase. Z. Naturforsch., B Chem. Sci. 56,386-393. 

Yonehara et al. [16] recently extended the scope of surfactant-promoted enantioselective hydrogenation on simple enamides. With respect to other reductive processes conducted in the presence of surfactants, it is noteworthy that the efficiency of an artifical nitrogenase model was selectively very enhanced by the addition of phospholipids [17]. 

Though these ideas appear to be attractive, for their acceptance direct experimental evidence for this nitrogenase model is required. 

The work on nitrogenase models was carried out in collaboration with my students, Gordon Schlesinger and Paul Doemeny. The studies on cobaloximes and cobalamins were carried out together with T. M. Beckham, J. W. Sibert, and J. H. Weber. The support of this work through the National Science Foundation is gratefully acknowledged. 

The participation of hydrazido(2—) (NNH2) and hydrazido(l —) (NHNHj) ligands in the protonation of coordinated Nj has been extensively discussed elsewhere and will not be considered in great detail here. A relatively brief discussion of the chemistry of hydrazide ligands in general was included in a 1983 account of the nitrogenase models, but the area has not been reviewed since. 

A nitrogenase model reaction has been accomplished in which significant amounts of NH3 (0.013-0.044 mol NH3/M0) are produced when trans-[Mo(N2)2(Ph2PCH2CH2PPh2)2] is added to[FeS(SCHPhCHPhS)]4 reduced to the 4 — or lower level. The molybdenum complex is also reducible by an excess of Na (naphthalene) to afford NH3 (0.100—0.300 mol NH3/M0). No N2H4 was observed in either reduction. The iron-dithiolen system alone is capable of fixing N2 at the 4— level under an N2 atmosphere NH3 up to... 

Today nitrogenase model chemistry has come quite a long way and some amazing science has been carried out. Still, we remain quite far away from being able to mimic the M-Cluster with all its features. This is partly due to the fact that for decades chemists tried to model a molybdenum-iron cluster, lacking an interstitial atom, now recognized to be carbon. 

The two components of the Fe-Mo protein nitrogenase, which is responsible for the fixation of nitrogen by microbes, have been purified and characterized from several sources. It seems that the enzyme acts through an elaborate mechanism which involves electron transport from one protein to the other promoted by reaction with Mg-ATP. Further results with a nitrogenase model have been reported. 

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